Watercraft propulsion system, watercraft, and power system

ABSTRACT

A watercraft propulsion system includes an engine, a propeller to be driven by the engine, a generator to be driven by the engine, a rectifier regulator connected to the generator, and a charging controller configured or programmed to control charging of a battery with power generated by the rectifier regulator such that an inductive voltage of the generator approaches one half an inter-terminal voltage of the battery.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to Japanese Patent Application No. 2022-071147 filed on Apr. 22, 2022. The entire contents of this application are hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a watercraft propulsion system, a watercraft, and a power system.

2. Description of the Related Art

An outboard motor, which is an example of a watercraft propulsion system, includes an engine and a propeller driven by the engine, and a propulsive force generated by the propeller is applied to a hull (US 2017/0012488 A1). The outboard motor further includes a starter motor that starts the engine, and a generator driven by the engine. The starter motor receives a power supply from a battery provided in the hull to be operative to crank the engine. After the completion of the start of the engine, the battery is charged with power generated by the generator. In a watercraft including a plurality of outboard motors, a plurality of batteries corresponding to the number of the outboard motors, typically the same number of batteries as that of the outboard motors, are provided in the hull.

The power required in the watercraft is not limited to that for the start of the starter motor. Specifically, nautical systems such as a navigation system and a fish finder also require a power supply. Further, apparatuses for passengers' activities and recreations on the watercraft require a power supply. Specific examples of such apparatuses include home electrical appliances such as a microwave oven, a refrigerator and an air conditioner. These electrical apparatuses are also dependent on the batteries provided in the hull for the power supply.

The batteries can be charged from a terrestrial power source when the watercraft is berthed in port. On the watercraft, the batteries can be charged with the power generated by the generator of the outboard motor.

As the power consumption on the watercraft increases, a greater number of batteries should be provided in the hull. However, the provision of the greater number of batteries reduces the size of usable space on the watercraft. In addition, the provision of the batteries increases the overall weight of the watercraft and, therefore, inevitably influences the movability (e.g., the ability to accelerate and turn) and the fuel efficiency of the watercraft.

SUMMARY OF THE INVENTION

The inventor of preferred embodiments of the present invention described and claimed in the present application conducted an extensive study and research regarding watercraft propulsion systems, such as the one described above, and in doing so, discovered and first recognized new unique challenges and previously unrecognized possibilities for improvements as described in greater detail below.

If a sufficient and satisfactory power generation system is provided on the watercraft, the electrical apparatuses can be used for a longer period of time with provision of a lower-capacity battery or a smaller number of batteries.

Preferred embodiments of the present invention provide watercraft propulsion systems that each improve a power generation efficiency of a generator provided therein, and watercrafts each including a watercraft propulsion system that solve the above-described problems. That is, the number of batteries to be provided on the watercraft may be reduced by improving the power generation efficiency of the watercraft propulsion system. Therefore, more usable space may be provided in the watercraft. In addition, the watercraft may have improved movability. Further, the watercraft may have a reduced weight to thus improve the fuel efficiency. Furthermore, the power generation efficiency is improved to thus improve the fuel efficiency. Consequently, this reduces the CO₂ emissions, thus making it possible to contribute to carbon neutrality and, thus, achieve some SDGs (Sustainable Development Goals).

Another preferred embodiment of the present invention provides a power system that improves the power generation efficiency of a generator driven by an engine. The improved power generation efficiency improves the fuel efficiency of the engine. This reduces the CO₂ emissions, thus making it possible to contribute to carbon neutrality and, thus, achieve some SDGs.

In order to overcome the previously unrecognized and unsolved challenges described above, a preferred embodiment of the present invention provides a watercraft propulsion system including an engine, a propeller to be driven by the engine, a generator to be driven by the engine, a rectifier regulator connected to the generator, and a charging controller configured or programmed to control the charging of a battery with a power generated by the rectifier regulator such that an inductive voltage of the generator approaches one half an inter-terminal voltage of the battery.

With this arrangement, the battery is charged with power generated by the generator while the control operation is performed so that the inductive voltage of the generator approaches one half the inter-terminal voltage of the battery. Thus, the power generation efficiency of the generator is increased during the charging of the battery. This makes it possible to reduce the sizes and the number of batteries to be provided on the watercraft. Therefore, more usable space may be provided in the watercraft. In addition, the watercraft may have improved movability. Further, the watercraft may have a reduced weight, such that the watercraft propulsion system has improved fuel efficiency. Furthermore, the power generation efficiency is improved to thus improve the fuel efficiency. Consequently, this reduces CO₂ emissions, thus making it possible to contribute to carbon neutrality and, thus, to achieve some of the SDGs.

The charging controller is preferably configured or programmed so that the inductive voltage of the generator can be substantially maintained in a range not lower than one half the inter-terminal voltage of the battery.

In a preferred embodiment of the present invention, the battery includes a first battery having a first inter-terminal voltage, and a second battery having a second inter-terminal voltage that is higher than the first inter-terminal voltage. The watercraft propulsion system further includes an engine rotation speed sensor to detect the rotation speed of the engine. The charging controller includes a switch to connect the rectifier regulator to either one of the first battery and the second battery, and a controller configured or programmed to control the switch according to the engine rotation speed detected by the engine rotation speed sensor.

With this arrangement, the battery to be charged with the power generated by the generator is switched between the first battery having a lower inter-terminal voltage and the second battery having a higher inter-terminal voltage. This switching operation is performed according to the engine rotation speed. The engine rotation speed corresponds to an inductive voltage generated by the generator. That is, the controller switches the to-be-charged battery between the first battery and the second battery based on the engine rotation speed so that the inductive voltage of the generator approaches one half the inter-terminal voltage of the battery. This makes it possible to charge the first battery and the second battery while properly maintaining the power generation efficiency of the generator.

The switch may be controllable in a first connection state in which the rectifier regulator is connected to the first battery, in a second connection state in which the rectifier regulator is connected to the second battery, or in a non-connection state in which the rectifier regulator is connected to neither the first battery nor the second battery. In this case, the controller preferably controls the switch in the first connection state, in the second connection state, or in the non-connection state according to the engine rotation speed. For example, the controller may control the switch in the non-connection state if the engine rotation speed falls within a lower rotation speed range in which the inductive voltage is lower than one half the first inter-terminal voltage.

In a preferred embodiment of the present invention, the watercraft propulsion system further includes a first power line through which the switch is connected to the first battery, and a second power line through which the switch is connected to the second battery. The charging controller further includes a boost converter connected between the first power line and the second power line. When the switch connects the rectifier regulator to the first battery, the controller is configured or programmed to activate or deactivate the boost converter depending on the residual capacity (e.g., the actual inter-terminal voltage) of the first battery.

With this arrangement, when the switch is connected to the first battery via the first power line and thus the first battery is charged, the boost converter boosts the voltage of the first power line and supplies voltage-boosted power to the second power line, such that the second battery can also be charged. The boost converter boosts a voltage occurring in the first power line to a voltage suitable for the charging of the second battery (typically, the inter-terminal voltage of the second battery).

In one specific example, if the residual capacity of the first battery exceeds a predetermined threshold, the controller activates the boost converter. Therefore, where the first battery is sufficiently charged, the second battery is simultaneously charged. Thus, the power generated by the generator is able to be efficiently stored and effectively utilized.

In a preferred embodiment of the present invention, the watercraft propulsion system further includes a first power line through which the switch is connected to the first battery, and a second power line through which the switch is connected to the second battery. The charging controller further includes a buck converter connected between the first power line and the second power line. When the switch connects the rectifier regulator to the second battery, the controller activates the buck converter.

With this arrangement, when the switch is connected to the second battery via the second power line and thus the second battery is charged, the buck converter reduces the voltage of the second power line and supplies voltage-reduced power to the first power line, such that the first battery is also able to be charged. Thus, the power generated by the generator is able to be efficiently stored and effectively utilized. The buck converter reduces a voltage occurring in the second power line to a voltage suitable for the charging of the first battery (typically, the inter-terminal voltage of the first battery).

The boost converter and the buck converter may include a boost-buck converter having both the boost function and the buck function. That is, the boost-buck converter may be operated in a boost mode to function as the boost converter, and may be operated in a buck mode to function as the buck converter. Of course, the boost converter and the buck converter may be separately provided.

In a preferred embodiment of the present invention, the watercraft propulsion system further includes an engine rotation speed sensor to detect the rotation speed of the engine. The charging controller includes a capacitor connected between terminals of the rectifier regulator, a buck converter to reduce the inter-terminal voltage of the capacitor and output a voltage-reduced power to the battery, and a controller configured or programmed to regulate the output power of the buck converter according to the engine rotation speed detected by the engine rotation speed sensor.

With this arrangement, the apparent inter-terminal voltage of the battery as observed from the generator is equal or substantially equal to the inter-terminal voltage of the capacitor. Therefore, the controller regulates the output power of the buck converter so that the inter-terminal voltage of the capacitor approaches one half the inductive voltage of the generator. This improves the power generation efficiency of the generator.

The capacitor is preferably an electrolytic capacitor or an electric double layer capacitor, more preferably the electric double layer capacitor. Not only the battery but also the capacitor are able to function as a storage battery that stores power to be used, for example, by the engine.

The buck converter reduces the inter-terminal voltage of the capacitor to a voltage suitable for the charging of the battery (typically, the inter-terminal voltage of the battery). Specifically, the output power of the buck converter may be regulated by regulating an output current.

The rectifier regulator regulates the voltage generated by the generator to a predetermined regulation voltage to output the regulation voltage.

US 2017/0012488 A1 discloses that the value of a DC voltage outputted from a rectifier regulator is controlled so that the power generation is increased with respect to the inductive voltage according to the engine rotation speed. In a preferred embodiment of the present invention, in contrast, such a voltage control operation is not performed to increase the power generation, but the power is outputted to the battery from the buck converter at a voltage suitable for the charging of the battery (typically, the inter-terminal voltage of the battery). In a preferred embodiment, the power generation efficiency of the generator is improved by regulating the output power of the buck converter so that the inter-terminal voltage of the capacitor approaches one half the inductive voltage of the generator.

More preferably, the output power of the buck converter is regulated to maintain the inter-terminal voltage of the capacitor in a range not lower than one half the inductive voltage of the generator. This makes it possible to maintain the inter-terminal voltage of the capacitor at not lower than the output voltage of the buck converter and thus to maintain the generator in a power extractable state.

In US 2017/0012488 A1 which involves the voltage control without the regulation of the output power, there is a possibility that the load is greater than the power generation. In order to maintain the highly efficient power generation, preferred embodiments of the present invention are more advantageous than US 2017/0012488 A1.

In a preferred embodiment of the present invention, the battery includes a first battery having a first inter-terminal voltage, and a second battery having a second inter-terminal voltage that is higher than the first inter-terminal voltage. The watercraft propulsion system further includes an engine rotation speed sensor to detect the rotation speed of the engine. The charging controller includes a capacitor connected between terminals of the rectifier regulator, a first buck converter to reduce the inter-terminal voltage of the capacitor and output a voltage-reduced power to the first battery, a second buck converter to reduce the inter-terminal voltage of the capacitor and output a voltage-reduced power to the second battery, and a controller configured or programmed to regulate the output power of the first buck converter according to the engine rotation speed detected by the engine rotation speed sensor, and to regulate the output power of the second buck converter according to an actual output power of the first buck converter and the engine rotation speed detected by the engine rotation speed sensor.

With this arrangement, the apparent inter-terminal voltage of the battery observed from the generator is equal or substantially equal to the inter-terminal voltage of the capacitor. Therefore, the controller regulates the output powers of the first buck converter and the second buck converter so that the inter-terminal voltage of the capacitor approaches one half the inductive voltage of the generator. This improves the power generation efficiency of the generator. As the engine rotation speed increases, the inductive voltage is increased and the power generated by the generator is increased. Therefore, the control operation is performed to regulate the output power of the second buck converter according to the engine rotation speed and the actual output power of the first buck converter, thus making it possible to charge both the first battery and the second battery while providing efficient power generation by the generator.

The first buck converter reduces the inter-terminal voltage of the capacitor to a voltage suitable for the charging of the first battery (typically, the inter-terminal voltage of the first battery). The second buck converter reduces the inter-terminal voltage of the capacitor to a voltage suitable for the charging of the second battery (typically, the inter-terminal voltage of the second battery). Specifically, the output powers of the first buck converter and the second buck converter may be regulated by regulating the output currents of the first buck converter and the second buck converter.

The rectifier regulator regulates the voltage generated by the generator to a predetermined regulation voltage, and outputs the regulation voltage.

More preferably, the output powers of the first buck converter and the second buck converter are regulated so that the inter-terminal voltage of the capacitor can be maintained in a range not lower than one half the inductive voltage of the generator. This makes it possible to maintain the inter-terminal voltage of the capacitor at not lower than the output voltage of the first buck converter and thus to maintain the generator in the power extractable state.

In a preferred embodiment of the present invention, the watercraft propulsion system includes an outboard motor.

Another preferred embodiment of the present invention provides a watercraft including a hull, a battery provided on the hull, and a watercraft propulsion system provided on the hull, wherein the watercraft propulsion system includes any of the above-described features.

In a preferred embodiment of the present invention, the watercraft further includes an electrical load provided on the hull and connected to the battery.

Another further preferred embodiment of the present invention provides a power system including an engine, a generator to be driven by the engine, a rectifier regulator connected to the generator, a battery to be charged with power generated by the rectifier regulator, and a charging controller configured or programmed to control the charging of the battery with the power generated by the rectifier regulator such that an inductive voltage of the generator approaches one half an inter-terminal voltage of the battery.

In a preferred embodiment of the present invention, the battery includes a first battery having a first inter-terminal voltage, and a second battery having a second inter-terminal voltage that is higher than the first inter-terminal voltage. The power system further includes an engine rotation speed sensor to detect the rotation speed of the engine. The charging controller includes a switch that connects the rectifier regulator to either one of the first battery and the second battery, and a controller configured or programmed to control the switch according to the engine rotation speed detected by the engine rotation speed sensor.

In a preferred embodiment of the present invention, the power system further includes a first power line through which the switch is connected to the first battery, and a second power line through which the switch is connected to the second battery. The charging controller further includes a boost converter connected between the first power line and the second power line. The controller activates or deactivates the boost converter depending on the residual capacity (the actual inter-terminal voltage) of the first battery when the switch connects the rectifier regulator to the first battery.

In a preferred embodiment of the present invention, the power system further includes a first power line through which the switch is connected to the first battery, and a second power line through which the switch is connected to the second battery. The charging controller further includes a buck converter connected between the first power line and the second power line. The controller activates the buck converter when the switch connects the rectifier regulator to the second battery.

In a preferred embodiment of the present invention, the power system further includes an engine rotation speed sensor to detect the rotation speed of the engine. The charging controller includes a capacitor connected between terminals of the rectifier regulator, a buck converter to reduce the inter-terminal voltage of the capacitor and output voltage-reduced power to the battery, and a controller configured or programmed to regulate the output power of the buck converter according to the engine rotation speed detected by the engine rotation speed sensor.

In a preferred embodiment of the present invention, the battery includes a first battery having a first inter-terminal voltage, and a second battery having a second inter-terminal voltage that is higher than the first inter-terminal voltage. The power system further includes an engine rotation speed sensor to detect the rotation speed of the engine. The charging controller includes a capacitor connected between terminals of the rectifier regulator, a first buck converter to reduce the inter-terminal voltage of the capacitor and output a voltage-reduced power to the first battery, a second buck converter to reduce the inter-terminal voltage of the capacitor and output a voltage-reduced power to the second battery, and a controller configured or programmed to regulate the output power of the first buck converter according to the engine rotation speed detected by the engine rotation speed sensor, and to regulate the output power of the second buck converter according to an actual output power of the first buck converter and the engine rotation speed detected by the engine rotation speed sensor.

The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view showing an exemplary structure of a watercraft including outboard motors according to one preferred embodiment of the present invention.

FIG. 2 is a schematic side view showing the structure of the outboard motor by way of example.

FIG. 3 is a block diagram showing the electrical configuration of a power system of the watercraft.

FIG. 4 is a diagram showing a relationship between power generated by an AC generator (power generation efficiency) and a battery voltage.

FIG. 5 is a characteristic diagram showing exemplary characteristic relationships between the rotation speed of an engine and the output power of the AC generator driven by the engine.

FIG. 6 shows an exemplary control operation to be performed by a controller shown in FIG. 3 .

FIG. 7 is a block diagram showing the electrical configuration of a watercraft power system according to another preferred embodiment of the present invention.

FIG. 8 shows an exemplary control operation to be performed by a controller shown in FIG. 7 .

FIG. 9 is a block diagram showing the electrical configuration of a watercraft power system according to further another preferred embodiment of the present invention.

FIG. 10 shows an exemplary control operation to be performed by a controller shown in FIG. 9 .

FIG. 11 is a block diagram showing the electrical configuration of a watercraft power system according to still another preferred embodiment of the present invention.

FIG. 12 shows an exemplary control operation to be performed by a controller shown in FIG. 11 .

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a schematic side view showing an exemplary structure of a watercraft (outboard motor watercraft) including outboard motors according to a preferred embodiment of the present invention. The watercraft 100 includes a hull 1, and outboard motors 2 provided as an example of the watercraft propulsion system on the hull 1. In this example, two outboard motors 2 are attached to the stern of the hull 1, and disposed side by side transversely of the hull 1.

The hull 1 includes a cabin 4 defined by an outer shell to provide a living area, and a deck 5 disposed behind the cabin 4 to provide an open usable space. A watercraft maneuvering station 6 is provided in the cabin 4. In the present preferred embodiment, a steering wheel 7 and acceleration levers 8 are provided in the watercraft maneuvering station 6. The steering wheel 7 is an operation element to steer the watercraft 100. The outboard motors 2 are turned leftward and rightward in response to the operation of the steering wheel 7 to change the directions of propulsive forces to be applied to the hull 1 leftward and rightward. The acceleration levers 8 are operation elements to adjust propulsive force. By operating the acceleration levers 8, the shift positions of the outboard motors 2 are each shifted to a forward shift position, a neutral shift position, or a reverse shift position, and the magnitudes of the propulsive forces to be generated by the outboard motors 2 are adjusted. In the present preferred embodiment, the outboard motors 2 are engine outboard motors each including an engine 21 to generate the propulsive force by the driving force of the engine 21. By operating the acceleration levers 8, the throttle opening degrees of the engines 21 are changed to correspondingly change the rotation speeds of the engines 21.

In the watercraft maneuvering station 6, main switches 10 to be operated by a user for the power-on of the outboard motors 2 are provided for the respective outboard motors 2. Further, start switches 11 to be operated by the user to start the engines 21 of the respective outboard motors 2 are provided for the respective outboard motors 2 in the watercraft maneuvering station 6. The main switches 10 and the start switches 11 may each include a rotation type operation element to be operated to turn on and off the main switch or turn on and off the start switch depending on the rotational position of the operation element.

One or more batteries 90 are provided on the hull 1. The batteries 90 are used to drive the starter motors of ISGs 63 to start the engines 21. The batteries 90 may be used to supply power to electrical apparatuses 13 (electrical loads) provided on the hull 1. The electrical apparatuses 13 may include nautical systems typified by a navigation system and a fish finder. Further, the electrical apparatuses 13 may include home electrical appliances such as a refrigerator, a microwave oven, and an air conditioner. The batteries 90 may include one or more first batteries 91 (typically, the same number of first batteries 91 as that of the outboard motors 2) to be used to start the engines 21, and one or more second batteries 92 to be used for the power supply to the electrical apparatuses 13 (particularly, the home electrical appliances). For example, the first batteries 91 may each conform to a voltage specification of a first inter-terminal voltage (e.g., 12 V). Further, the second batteries 92 may each conform to a voltage specification of a second inter-terminal voltage (e.g., 48 V) that is higher than the first inter-terminal voltage. The batteries 90 are typically lead storage batteries, but may be storage batteries of other types such as lithium ion batteries.

A fuel for the outboard motors 2 is typically stored in a fuel tank 14 provided on the hull 1, and supplied to the outboard motors 2 from the fuel tank 14.

FIG. 2 is a schematic side view showing the structure of the outboard motor 2 by way of example. The outboard motor 2 is an engine outboard motor including the engine 21 (internal combustion engine) as its drive source. The outboard motor 2 includes an outboard motor body 20 and an attachment mechanism 28. The outboard motor body 20 is attached to the stern of the hull 1 by the attachment mechanism 28. The attachment mechanism 28 includes a swivel bracket 54, a pair of clamp brackets 55, a steering shaft 56, and a tilt shaft 57. The steering shaft 56 extends vertically. The tilt shaft 57 is oriented generally horizontally and extending laterally. The swivel bracket 54 is connected to the outboard motor body 20 via the steering shaft 56. The pair of clamp brackets 55 are laterally spaced apart. The clamp brackets 55 clamp an attachment plate 3 provided on the stern of the hull 1, and serve as fastening members to fasten the outboard motor body 20 to the hull 1.

The outboard motor body 20 is attached in a generally vertical attitude to the hull 1 by the attachment mechanism 28. The outboard motor body 20 and the swivel bracket 54 are able to pivot about the tilt shaft 57 up and down with respect to the clamp brackets 55. The outboard motor body 20 and the swivel bracket 54 are pivoted about the tilt shaft 57 up and down by a tilt/trim mechanism 58. Further, the outboard motor body 20 is able to pivot about the steering shaft 56 leftward and rightward with respect to the swivel bracket 54. The outboard motor body 20 is pivoted about the steering shaft 56 according to the operation of the steering wheel 7 to thus steer the watercraft 100.

The outboard motor body 20 includes the engine 21, a drive shaft 41, a propeller shaft 42, a propeller 43, a forward/reverse switching mechanism 44, an ECU (electronic control unit) 60, and the ISG (Integrated Starter Generator, motor generator) 63. The outboard motor body 20 includes an engine cover 37 and a casing 38. The engine 21, the ECU 60, and the ISG 63 are accommodated in the engine cover 37.

The engine 21 is disposed with its crank shaft 22 extending vertically. The drive shaft 41 is connected to the crank shaft 22. The drive shaft 41 extends vertically in the engine cover 37 and the casing 38. The propeller shaft 42 extends horizontally (anteroposteriorly) in the casing 38. The upper end of the drive shaft 41 is connected to the crank shaft 22, and the lower end of the drive shaft 41 is connected to the propeller shaft 42 via the forward/reverse switching mechanism 44 in a power transmittable manner. The forward/reverse switching mechanism 44 is a transmission mechanism that transmits the rotation of the drive shaft 41 to the propeller shaft 42. The propeller 43 is connected to the rear end of the propeller shaft 42. Therefore, the propeller 43 is rotated together with the propeller shaft 42. The power of the engine 21 is transmitted to the propeller 43 via the drive shaft 41, the forward/reverse switching mechanism 44, and the propeller shaft 42 to rotate the propeller 43.

The forward/reverse switching mechanism 44 includes a driving gear 45, a forward gear 46, a reverse gear 47, a dog clutch 48, and a shift mechanism 50. The driving gear 45, the forward gear 46, and the reverse gear 47 are bevel gears. The driving gear 45 is fixed to the lower end of the drive shaft 41. The forward gear 46 and the reverse gear 47 are provided around the front end portion of the propeller shaft 42, and the propeller shaft 42 extends through the forward gear 46 and the reverse gear 47. The forward gear 46 and the reverse gear 47 are rotatable with respect to the propeller shaft 42. The forward gear 46 and the reverse gear 47 are constantly engaged with the driving gear 45. By rotating the driving gear 45, the forward gear 46 and the reverse gear 47 are rotated in opposite directions on the propeller shaft 42.

The forward gear 46 and the reverse gear 47 are spaced from each other axially along the propeller shaft 42, and the dog clutch 48 is disposed between the forward gear 46 and the reverse gear 47. The dog clutch 48 is a slider which is spline-connected to the propeller shaft 42 to be rotatable together with the propeller shaft 42 and anteroposteriorly slidable axially along the propeller shaft 42. The dog clutch 48 is moved anteroposteriorly axially along the propeller shaft 42 by the shift mechanism 50. The shift mechanism 50 includes, for example, a shift rod 51 extending vertically, a shift actuator 52 connected to the upper end of the shift rod 51, and a shift position sensor 53 to detect the position of the dog clutch 48 as the shift position. The shift actuator 52 operates according to the operation of the acceleration lever 8 (see FIG. 1 ). The shift rod 51 is pivoted by the shift actuator 52, such that the dog clutch 48 is moved axially along the propeller shaft 42. Thus, the dog clutch 48 is located at one of the forward shift position, the reverse shift position, and the neutral shift position. At the forward shift position, the dog clutch 48 is meshed with the forward gear 46, such that the propeller shaft 42 and the propeller 43 are rotated in a forward drive direction. At the reverse shift position, the dog clutch 48 is meshed with the reverse gear 47, such that the propeller shaft 42 and the propeller 43 are rotated in a reverse drive direction. At the neutral shift position, the dog clutch 48 is meshed with neither the forward gear 46 nor the reverse gear 47, such that the power is not transmitted between the drive shaft 41 and the propeller shaft 42.

The engine 21 is an internal combustion engine that generates the power by combustion of the fuel. The engine 21 includes the crank shaft 22, a plurality of cylinders 23 (e.g., four cylinders 23), and a cylinder block 24 accommodating the crank shaft 22 and the cylinders 23. The cylinder block 24 includes a cylinder head 25, a cylinder body 26, and a crank case 27. The crank shaft 22 is rotated about its vertical axis by the combustion in the cylinders 23. The rotation speed of the crank shaft 22 (engine rotation speed) is detected by an engine rotation speed sensor 59. The engine rotation speed sensor 59 may be a crank angle sensor that outputs a detection signal (crank pulse) in synchronism with the rotation of the crank shaft 22, and the ECU 60 may process the output signal to detect the engine rotation speed.

The engine 21 includes a plurality of ignition plugs 35 provided for the respective cylinders 23, and a plurality of ignition coils (not shown) respectively connected to the ignition plugs 35. The engine 21 further includes a plurality of fuel injectors 31 provided for the respective cylinders 23. The engine 21 further includes a fuel pump 32 that supplies the fuel to the fuel injectors 31. The fuel injectors 31 and the fuel pump 32 constitute a fuel supply system 30. The fuel pump 32 pumps up the fuel from the fuel tank 14 disposed on the hull 1 to supply the fuel to the fuel injectors 31. The ECU 60 performs an ignition control operation to cause the ignition plugs 35 to spark at proper timings, and performs a fuel injection control operation to inject a proper amount of the fuel from the fuel injectors 31 at proper timings.

FIG. 3 shows the electrical configuration of a power system of the watercraft 100. The ISG 63 is connected to the crank shaft 22 of the engine 21, and functions as a starter motor (not shown) that cranks the engine 21 and as an AC generator 62 that generates power by the rotation of the engine 21 (the rotation of the crank shaft 22). A rectifier regulator 70 is connected to the AC generator 62. The rectifier regulator 70 includes a rectification circuit 71 that rectifies AC power generated by the AC generator 62, and a regulation circuit 72 that regulates the upper limit of the output voltage to a predetermined regulation voltage. In the present preferred embodiment, the rectification circuit 71 includes a diode bridge. In the present preferred embodiment, the AC generator 62 is a three-phase AC generator, and the diode bridge correspondingly has a three-phase configuration. The regulation circuit 72 includes thyristors 73 that cause a short circuit between the phases of the AC generator 62, and a regulation control circuit 74 that controls the on/off of the thyristors 73. The regulation control circuit 74 may be operative to change the regulation voltage according to the engine rotation speed detected by the engine rotation speed sensor 59.

The positive terminal 70 a of the rectifier regulator 70 is connected to the positive terminal of the first battery 91 via a switching unit 83 and a first power line 81, and connected to the positive terminal of the second battery 92 via the switching unit 83 and a second power line 82. The negative terminal of the first battery 91 and the negative terminal of the second battery 92 are connected to the negative terminal 70 b of the rectifier regulator 70 via a ground line 85.

The switching unit 83 connects the rectifier regulator 70 to the first power line 81 or the second power line 82. Specifically, the switching unit 83 includes a plurality of switching devices 84. The switching devices 84 may each be a power semiconductor device such as power MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor). A controller 86 is provided to control the switching unit 83. The controller 86 controls the switching unit 83 according to the engine rotation speed detected by the engine rotation speed sensor 59. The switching unit 83 and the controller 86 constitute a charging controller 80 that charges the first battery 91 and the second battery 92 with the power generated by the AC generator 62. The ECU 60 may function as the controller 86. The controller 86 may typically be configured as including a processor, and a memory that stores a program to be executed by the processor.

FIG. 4 is a diagram showing a relationship between the power generated by the AC generator (power generation efficiency) and the battery voltage. Power Pg (W) generated by the AC generator is represented by the following expression (1) based on the inductive voltage e (open terminal voltage) and the impedance Z of a stator coil and the battery voltage V_(bat) (inter-terminal voltage), and is shown by a line Lg in FIG. 4 . Therefore, where the battery voltage V_(bat) of the battery to be charged is one half the inductive voltage e of the AC generator, i.e., where the inductive voltage e is twice the battery voltage V_(bat), the power generated by the AC generator (i.e., the power generation efficiency of the AC generator) is maximized. On the other hand, a power loss due to the stator coil (i.e., a so-called copper loss Pc (W)) is represented by the following expression (2) based on the electrical resistance R of the stator coil, and is shown by a line Lc in FIG. 4 . Therefore, the copper loss Pc is increased, as the ratio of the battery voltage V_(bat) to the inductive voltage decreases, i.e., as the ratio of the inductive voltage to the battery voltage V_(bat) increases. Where the copper loss Pc is not less than the generated power Pg, it is impossible to extract the power.

Pg=(−1/Z)×(V _(bat)−(e/2))²+(e ²/(4Z))   (1)

Pc=(R/Z ²)×(V _(bat) −e)²   (2)

In order to provide highly efficient power generation, therefore, a control target is to maintain the battery voltage in a range not lower than one half the inductive voltage, i.e., to maintain the inductive voltage in a range not higher than twice the battery voltage, and to cause the relationship between the battery voltage and the inductive voltage to approach a relationship such that the battery voltage is one half the inductive voltage, i.e., such that the inductive voltage is twice the battery voltage.

FIG. 5 shows exemplary characteristic relationships between the engine rotation speed and the output power of the AC generator driven by the engine. A line L12 indicates an exemplary generation power characteristic observed when the AC generator is connected to a battery having an inter-terminal voltage of 12 V, and a line L28 indicates an exemplary generation power characteristic observed when the AC generator is connected to a battery having an inter-terminal voltage of 28 V. A line L48 indicates an exemplary generation power characteristic observed when the AC generator is connected to a battery having an inter-terminal voltage of 48 V. With the AC generator connected to the 12-V battery, the output power increases in a lower rotation speed range, but is saturated in the lower rotation speed range. With the AC generator connected to the 48-V battery, on the other hand, no power is outputted in the lower rotation speed range, but the output power increases in an intermediate rotation speed range and is significantly increased in a higher rotation speed range. With the AC generator connected to the 28-V battery, the generation power characteristic is intermediate between that for the 12-V battery and that for the 48-V battery. That is, no power is outputted in the lower rotation speed range, but relatively high output power is generated in the intermediate rotation speed range. Since the inductive voltage of the AC generator is generally proportional to the engine rotation speed, the characteristic relationships shown in FIG. 5 may be regarded as indicating relationships between the inductive voltage and the generated power.

The characteristic relationships described above indicate that the lower rotation speed range is suitable for the charging of the 12-V battery, that the intermediate rotation speed range is suitable for the charging of the 28-V or 48-V battery, and that the higher speed rotation speed range is suitable for the charging of the 48-V battery.

FIG. 6 shows an exemplary control operation to be performed to control the switching unit 83 by the controller 86, and also shows a voltage regulation operation (regulation operation) to be performed by the rectifier regulator 70.

The controller 86 controls the switching unit 83 so as to connect the rectifier regulator 70 to one of the first power line 81 and the second power line 82 based on the engine rotation speed detected by the engine rotation speed sensor 59. More specifically, the switching unit 83 is configured to be controlled into a first connection state in which the rectifier regulator 70 is connected to the first power line 81, a second connection state in which the rectifier regulator 70 is connected to the second power line 82, and a non-connection state (cut-off state) in which the rectifier regulator 70 is connected to neither the first power line 81 nor the second power line 82. The controller 86 controls the switching unit 83 in the first connection state, the second connection state, or the non-connection state depending on the engine rotation speed. Specifically, if the engine rotation speed is lower than a predetermined first threshold (e.g., 650 rpm in the specific example shown in FIG. 6 ), the controller 86 controls the switching unit 83 in the non-connection state. Further, if the engine rotation speed is not lower than the first threshold and lower than a predetermined second threshold (e.g., 2,000 rpm in the specific example shown in FIG. 6 ), the controller 86 controls the switching unit 83 in the first connection state to connect the rectifier regulator 70 to the first battery 91 via the first power line 81. If the engine rotation speed is not lower than the second threshold, the controller 86 controls the switching unit 83 in the second connection state to connect the rectifier regulator 70 to the second battery 92 via the second power line 82.

Thus, the AC generator 62 generates the power according to the characteristic line L12 shown in FIG. 5 if the engine rotation speed falls within a lower rotation speed range (lower than 2,000 rpm), and generates the power according to the characteristic line L48 shown in FIG. 5 if the engine rotation speed falls within an intermediate to higher rotation speed range (not lower than 2,000 rpm). From another aspect, the battery 90 to be charged is switched between the batteries 91 and 92 as described above, such that the charging control operation is performed so that the inductive voltage can substantially approach twice the inter-terminal voltage of the battery 90. Thus, the AC generator 62 is able to efficiently generate the power.

When the engine rotation speed is lower than 650 rpm, there is a possibility that the inductive voltage of the AC generator 62 is lower than twice the inter-terminal voltage of the first battery 91. If the engine rotation speed falls within such a very low rotation speed range, therefore, the switching unit 83 is controlled in the non-connection state (cut-off state) to maintain the AC generator 62 in a power extractable state.

If the engine rotation speed falls within the lower rotation speed range (e.g., lower than 2,000 rpm), the regulation control circuit 74 of the rectifier regulator 70 controls the regulation voltage at a first level (e.g., about 14.5 V) to prevent the application of an over-voltage to the first battery 91 having an inter-terminal voltage of 12 V. Further, if the engine rotation speed falls within the intermediate to higher rotation speed range (e.g., not lower than 2,000 rpm), the regulation control circuit 74 controls the regulation voltage at a second level (e.g., about 58 V) that is higher than the first level. Thus, the application of a high voltage to the second power line 82 is prevented which may otherwise cause an electric shock.

FIG. 7 shows the electrical configuration of a watercraft power system according to another preferred embodiment of the present invention. In FIG. 7 , components corresponding to those shown in FIG. 3 will be denoted by the same reference characters as in FIG. 3 . In the present preferred embodiment, the charging controller 80 further includes a boost-buck converter 110 (DC/DC converter) connected between the first power line 81 and the second power line 82. The controller 86 controls the operation of the boost-buck converter 110. More specifically, the controller 86 activates or deactivates the boost function of the boost-buck converter 110 (a function as a boost converter) depending on the residual capacity (more specifically, the actual inter-terminal voltage) of the first battery 91 when the switching unit 83 connects the rectifier regulator 70 to the first battery 91. Further, the controller 86 activates the buck function of the boost-buck converter 110 (a function as a buck converter) when the switching unit 83 connects the rectifier regulator 70 to the second battery 92.

The boost-buck converter 110 includes an inductor 111 (choke coil) connected between the first power line 81 and the second power line 82, a first switching device 112, and a second switching device 113. The first switching device 112 is connected between the inductor 111 and the ground line 85. The second switching device 113 is connected between the inductor 111 and the second power line 82. More specifically, the first switching device 112 is connected between the ground line 85 and a terminal of the inductor 111 opposite from the first power line 81.

The controller 86 performs a boost operation by controlling the switching of the first switching device 112 and the second switching device 113 in a boost mode. Thus, the boost-buck converter 110 boosts the voltage of power occurring in the first power line 81 to a voltage level suitable for the charging of the second battery 92 (typically, the inter-terminal voltage of the second battery 92), and supplies voltage-boosted power to the second battery 92. Similarly, the controller 86 performs a buck operation by controlling the switching of the first switching device 112 and the second switching device 113 in a buck mode. Thus, the boost-buck converter 110 reduces the voltage of power occurring in the second power line 82 to a voltage level suitable for the charging of the first battery 91 (typically, the inter-terminal voltage of the first battery 91), and supplies voltage-reduced power to the first battery 91.

The first switching device 112 and the second switching device 113 may each be a power semiconductor device such as power MOSFET.

FIG. 8 shows an exemplary control operation to be performed by the controller 86 to control the switching unit 83 and the boost-buck converter 110. The switching unit 83 is controlled according to the engine rotation speed in the same manner as in FIG. 6 and, therefore, the description thereof will be omitted. The regulation voltage of the rectifier regulator 70 is also controlled in the same manner as in FIG. 6 and, therefore, the description thereof will be omitted.

In this example, the actual inter-terminal voltage of the first battery 91 is used as an index of the residual capacity of the first battery 91. The actual inter-terminal voltage of the first battery 91 having a nominal inter-terminal voltage of 12 V is detected by a voltage sensor 115 (see FIG. 7 ). If the actual inter-terminal voltage is not lower than about 13.6 V, for example, it is considered that the first battery 91 is in a sufficiently charged state (in which the residual charge capacity is not lower than a charging end threshold). If the actual inter-terminal voltage is not higher than about 13.0 V, for example, on the other hand, it is considered that the first battery 91 is in a preferential charging residual capacity state (in which the residual charge capacity is not higher than a charging start threshold) for the start of the engine 21 (for the cranking of the engine 21 by the starter motor).

If the engine rotation speed falls within the very low rotation speed range (e.g., lower than 650 rpm) in which the switching unit 83 is in the non-connection state, the controller 86 deactivates the boost function and the buck function of the boost-buck converter 110. If the engine rotation speed falls within the lower rotation speed range (e.g., lower than 2,000 rpm) in which the switching unit 83 connects the rectifier regulator 70 to the first power line 81, the controller 86 activates the boost function of the boost-buck converter 110. In other words, when the switching unit 83 connects the rectifier regulator 70 to the first power line 81, the controller 86 activates the boost function of the boost-buck converter 110. When the engine rotation speed falls within the intermediate to higher rotation speed range (e.g., not lower than 2,000 rpm), the switching unit 83 supplies the power to the second battery 92 via the second power line 82 and, therefore, the controller 86 maintains the boost-buck converter 110 in a boost function deactivation state.

If the actual inter-terminal voltage of the first battery 91 is not lower than 13.6 V, for example, when the switching unit 83 supplies the power to the first power line 81, the controller 86 activates the boost function of the boost-buck converter 110. Therefore, the power is also supplied to the second power line 82 from the first power line 81, so that the first battery 91 and the second battery 92 are simultaneously charged. If the actual inter-terminal voltage of the first battery 91 is not higher than 13.0 V, for example, when the engine rotation speed falls within the lower rotation speed range, the controller 86 controls the boost-buck converter 110 in the boost function deactivation state. Therefore, the second battery 92 is not charged, but the first battery 91 is preferentially charged for the engine start.

When the engine rotation speed falls within the intermediate to higher rotation speed range, the controller 86 causes the switching unit 83 to connect the rectifier regulator 70 to the second power line 82. At this time, the controller 86 deactivates the boost function of the boost-buck converter 110, and activates the buck function of the boost-buck converter 110. Thus, the second battery 92 and the first battery 91 are simultaneously charged.

Since the voltage to be outputted from the rectifier regulator 70 is not higher than 60 V, it is possible to use a non-insulation type DC/DC converter having a smaller size and a lighter weight as the boost-buck converter 110.

FIG. 9 shows the electrical configuration of a watercraft power system according to another further preferred embodiment of the present invention. In FIG. 9 , components corresponding to those shown in FIG. 3 will be denoted by the same reference characters as in FIG. 3 .

In the present preferred embodiment, the charging controller 80 includes a capacitor 125 connected between the positive terminal 70 a and the negative terminal 70 b of the rectifier regulator 70, and a buck converter 120 (DC/DC converter) that reduces the inter-terminal voltage of the capacitor 125 and supplies voltage-reduced power to the battery 90. The battery 90 is herein the first battery 91 having a nominal inter-terminal voltage of 12 V and is, for example, a lead storage battery. The buck converter 120 reduces the inter-terminal voltage of the capacitor 125 to a voltage level suitable for the charging of the battery 90 (typically, the inter-terminal voltage of the first battery 91). The controller 86 regulates the output power of the buck converter 120 depending on the engine rotation speed detected by the engine rotation speed sensor 59. Specifically, the output power may be regulated by regulating an output current.

The capacitor 125 may be, for example, an electrolytic capacitor or an electric double layer capacitor. More preferably, the capacitor 125 is the electric double layer capacitor. Where the electric double layer capacitor is used as the capacitor 125, not only the battery 90 but also the capacitor 125 are able to function as a storage battery that stores power to be used by the electrical components of the engine 21. The electric double layer capacitor is smaller in size and lighter in weight than an electrolytic capacitor having the same capacity and, therefore, can be advantageously mounted in the outboard motor 2.

The buck converter 120 includes a switching device 121 connected between the positive terminal of the capacitor 125 and the positive terminal of the battery 90, and an inductor 122 (choke coil) and a diode 123 connected in parallel between a power line 81 and a ground line 85 at a position between the switching device 121 and the battery 90. The diode 123 is connected between the power line 81 and the ground line 85 with its forward direction extending from the ground line 85 to the power line 81. The switching device 121 may be a power semiconductor device such as power MOSFET. The controller 86 controls the on/off of the switching device 121, such that the inter-terminal voltage of the capacitor 125 is reduced to the inter-terminal voltage of the battery 90 (e.g., 12 V) and voltage-reduced power is supplied to the battery 90.

The rectifier regulator 70 is operative so that the upper limit of its inter-terminal voltage is 60 V. That is, the rectifier regulator 70 generates a voltage of 0 V to 60 V according to the engine rotation speed, and the inter-terminal voltage of the capacitor 125 correspondingly varies in a voltage range of 0 V to 60 V. When the inter-terminal voltage of the capacitor 125 falls within a range of 12 V to 60 V, i.e., when the inter-terminal voltage of the capacitor 125 is not lower than the inter-terminal voltage of the battery 90 (first battery 91), the buck converter 120 reduces the voltage to 12 V and outputs a reduced-voltage power to the battery 90.

The controller 86 of the charging controller 80 is operative to regulate the output power by the on/off control of the switching device 121, such that the AC generator 62 is able to generate the greatest possible power.

The apparent inter-terminal voltage of the battery 90 as observed from the AC generator 62 is equal or substantially equal to the inter-terminal voltage of the capacitor 125. Therefore, the controller 86 regulates the output power of the buck converter 120 so that the inter-terminal voltage of the capacitor 125 approaches one half the inductive voltage of the AC generator 62. This makes it possible to efficiently extract the power from the AC generator 62.

FIG. 10 shows an exemplary output regulation control operation to be performed by the controller 86 to regulate the output of the buck converter 120, and also shows a voltage regulation operation (regulation operation) to be performed by the rectifier regulator 70. The inductive voltage for the engine rotation speed is also shown. Here, the inductive voltage is an inductive voltage appearing at a terminal (open termina) of the stator coil of the AC generator 62 when the stator coil is open and the engine rotation speed is at the lower limit value of each of the engine rotation speed ranges. In general, the value of the inductive voltage is not detectable in the actual system but, if necessary, can be determined by calculation based on the detected engine rotation speed.

The controller 86 performs the output regulation control operation to regulate the output of the buck converter 120 according to the engine rotation speed detected by the engine rotation speed sensor 59. Specifically, an output limit value is set according to the engine rotation speed, and the output power of the buck converter 120 is regulated at not higher than the output limit value.

More specifically, if the engine rotation speed falls within an engine rotation speed range of not lower than 0 rpm and lower than 650 rpm, the controller 86 sets the output power limit value to 0 W. That is, the buck converter 120 outputs no power. With the engine rotation speed within this range, there is a possibility that the inter-terminal voltage of the capacitor 125 cannot be maintained in a range higher than one half the inductive voltage of the AC generator 62. With the engine rotation speed within the range from 0 rpm to 650 rpm, the inter-terminal voltage of the capacitor 125 can be maintained at not lower than the output voltage of the buck converter 120 by stopping the output of the power from the buck converter 120, so that the AC generator 62 can be maintained in a power extractable state to thus prevent a power failure.

For example, if the engine rotation speed falls within an engine rotation speed range of not lower than 650 rpm, to lower than 1,000 rpm, the controller 86 sets the output power limit value to 750 W. If the engine rotation speed falls within an engine rotation speed range of not lower than 1,000 rpm, and lower than 1,500 rpm, the controller 86 sets the output power limit value to 1,200 W. If the engine rotation speed falls within an engine rotation speed range of not lower than 1,500 rpm and lower than 2,000 rpm, the controller 86 sets the output power limit value to 2,300 W. If the engine rotation speed falls within an engine rotation speed range of not lower than 2,000 rpm and lower than 3,000 rpm, the controller 86 sets the output power limit value to 2,800 W. If the engine rotation speed falls within an engine rotation speed range of not lower than 3,000 rpm and lower than 6,000 rpm, the controller 86 sets the output power limit value to 4,200 W. If the engine rotation speed falls within an engine rotation speed range of not lower than 6,000 rpm, the controller 86 sets the output power limit value to 4,700 W. For each of the engine rotation speed ranges, the buck converter 120 supplies the power at a level of not higher than the output power limit value to the battery 90.

In FIG. 5 described above, a characteristic line C3 of the output limit value with respect to the engine rotation speed is also shown. The characteristic line C3 indicates that the output limit value changes stepwise with respect to the engine rotation speed. As shown, the characteristic line C3 changes stepwise so that the output power can be regulated to permit the power generation substantially according to the line L12 in a lower rotation speed range from 0 rpm to 1,000 rpm, to permit the power generation substantially according to the line L28 in an intermediate rotation speed range from 1,000 rpm to 2,000 rpm, and to permit the power generation substantially according to the line L48 in a higher rotation speed range above 3,000 rpm. That is, the output power of the buck converter 120 is regulated according to the engine rotation speed, i.e., according to the inductive voltage of the AC generator 62, such that the AC generator 62 is able to efficiently generate the power. Of course, the output limit values are set as shown in FIG. 10 and as shown by the characteristic line C3 in FIG. 5 by way of example. If narrower engine rotation speed ranges are defined, for example, the characteristic lines can conform more closely to the lines L12, L28, L48 in the respective engine rotation speed ranges.

By thus regulating the output power of the buck converter 120, the apparent inter-terminal voltage of the battery 90 as observed from the AC generator 62, i.e., the inter-terminal voltage of the capacitor 125, can be controlled to be substantially maintained at one half the inductive voltage of the AC generator 62. Thus, the power can be efficiently extracted from the AC generator 62.

As shown in FIG. 10 , the regulation voltage of the rectifier regulator 70 is constant at 60 V. However, if the engine rotation speed falls within the engine rotation speed range lower than 1,000 rpm, the inductive voltage does not reach 60 V and, therefore, the output regulation control operation is not performed.

US 2017/0012488 A1 discloses that the value of the DC voltage outputted from the rectifier regulator is controlled so that the power generation is increased with respect to the inductive voltage according to the engine rotation speed. In the present preferred embodiment, in contrast, the rectifier regulator 70 does not perform such a voltage control operation to increase the power generation, but simply performs the regulation operation for the prevention of an electric shock. The power is supplied from the buck converter 120 to the battery 90 at a voltage level suitable for the charging of the battery 90 (at the inter-terminal voltage of the first battery 91). By regulating the output power of the buck converter 120, the inter-terminal voltage of the capacitor 125 approaches one half the inductive voltage of the AC generator 62. Thus, the power generation efficiency of the AC generator 62 is increased.

In the present preferred embodiment, the output power of the buck converter 120 is regulated so that the inter-terminal voltage of the capacitor 125 can be maintained in a range not lower than one half the inductive voltage of the AC generator 62. Specifically, if the engine rotation speed falls within the very low rotation speed range lower than 650 rpm, the buck converter 120 outputs no power. Thus, the inter-terminal voltage of the capacitor 125 can be maintained at not lower than the output voltage of the buck converter 120, so that the AC generator 62 can be maintained in the power extractable state to thus prevent the power failure.

In US 2017/0012488 A1 which does not perform the output power regulation operation but performs the voltage control operation, there is a possibility that the load is greater than the power generation. Therefore, preferred embodiments of the present invention are able to more easily maintain the highly efficient power generation.

Since the voltage to be outputted from the rectifier regulator 70 is not higher than 60 V, it is possible to use a non-insulation type DC/DC converter having a smaller size and a lighter weight as the buck converter 120. In US 2017/0012488 A1, the output voltage of the rectifier regulator is higher than 60 V, so that an insulation type DC/DC converter having a greater size and a heavier weight may be necessary.

FIG. 11 shows the electrical configuration of a watercraft power system according to still another preferred embodiment of the present invention. In FIG. 11 , components corresponding to those shown in FIG. 7 will be denoted by the same reference characters as in FIG. 7 . In the present preferred embodiment, a second battery 92 having an inter-terminal voltage of 48 V is mounted in addition to the first battery 91 having an inter-terminal voltage of 12 V on the watercraft 100 (see FIG. 1 ). Not only the first battery 91 but also the second battery 92 is charged with the power generated by the AC generator 62. The first battery 91 and the second battery 92 are, for example, lead storage batteries. A first buck converter 130 (DC/DC converter) and a second buck converter 140 (DC/DC converter) are provided to convert the power generated by the AC generator 62 to voltages suitable for the charging of the first battery 91 and the second battery 92 (specifically, the inter-terminal voltages of the first battery 91 and the second battery 92). The controller 86 regulates the output power of the first buck converter 130 according to the engine rotation speed detected by the engine rotation speed sensor 59. Further, the controller 86 regulates the output power of the second buck converter 140 according to the engine rotation speed and the actual output power of the first buck converter 130. Specifically, the output powers of the first buck converter 130 and the second buck converter 140 may be each regulated by regulating an output current.

The rectifier regulator 70 is configured and is operative in the same manner as in the preferred embodiment shown in FIG. 7 .

The first buck converter 130 functions in the same manner as the buck converter 120 shown in FIG. 9 . That is, the first buck converter 130 reduces the inter-terminal voltage of the capacitor 125 to the inter-terminal voltage of the first battery 91, and supplies the voltage-reduced power to the first battery 91. More specifically, when the inter-terminal voltage of the capacitor 125 falls within a range of 12 V to 60 V, i.e., is not lower than the inter-terminal voltage of the first battery 91, the first buck converter 130 reduces the voltage to 12 V and outputs the voltage-reduced power to the first battery 91. The first buck converter 130 includes a switching device 131 and an inductor 132 (choke coil) connected in series between the positive terminal of the capacitor 125 and the positive terminal of the first battery 91. The first buck converter 130 further includes a diode 133 having a cathode connected between the switching device 131 and the inductor 132 and an anode connected to the ground line 85. The switching device 131 may be a power semiconductor device such as power MOSFET. The controller 86 controls the on/off of the switching device 131, such that the inter-terminal voltage of the capacitor 125 is reduced and the voltage-reduced power is supplied to the first battery 91.

When the inter-terminal voltage of the capacitor 125 falls within a range of 12 V to 60 V, more specifically, when the inter-terminal voltage of the capacitor 125 is not lower than the inter-terminal voltage of the second battery 92, the second buck converter 140 reduces its voltage to the inter-terminal voltage of the second battery 92 (specifically, 48 V), and supplies the voltage-reduced power to the second battery 92. The second buck converter 140 includes a switching device 141 and an inductor 142 (choke coil) connected in series between the positive terminal of the capacitor 125 and the positive terminal of the first battery 91. The second buck converter 140 further includes a diode 143 having a cathode connected between the switching device 141 and the inductor 142 and an anode connected to the ground line 85. The switching device 141 may be a power semiconductor device such as power MOSFET. The controller 86 controls the on/off of the switching device 141, such that the inter-terminal voltage of the capacitor 125 is reduced and the voltage-reduced power is supplied to the second battery 92.

The controller 86 is able to regulate the output power of the first buck converter 130 by turning on and off the switching device 131 of the first buck converter 130. Further, the controller 86 is able to regulate the output power of the second buck converter 140 by turning on and off the switching device 141 of the second buck converter 140. Thus, the controller 86 is operative so that the AC generator 62 can generate the greatest possible power. The apparent inter-terminal voltage of the battery 90 as observed from the AC generator 62 is the inter-terminal voltage of the capacitor 125. Therefore, the controller 86 regulates the output powers of the first buck converter 130 and the second buck converter 140 so that the inter-terminal voltage of the capacitor 125 approaches one half the inductive voltage of the AC generator 62. Thus, the power can be efficiently extracted from the AC generator 62.

FIG. 12 shows an exemplary output regulation control operation to be performed on the first buck converter 130 and the second buck converter 140 by the controller 86, and also shows a voltage regulation operation (regulation operation) to be performed by the rectifier regulator 70. As in FIG. 10 , the inductive voltage (open terminal voltage) for the engine rotation speed is also shown in FIG. 12 .

The controller 86 performs the output regulation control operation on the first buck converter 130 according to the engine rotation speed detected by the engine rotation speed sensor 59. Specifically, the controller 86 sets a first output limit value for the first buck converter 130 according to the engine rotation speed, and regulates the output power of the first buck converter 130 at not higher than the first output limit value.

More specifically, if the engine rotation speed falls within an engine rotation speed range of not lower than 0 rpm and lower than 650 rpm, the controller 86 sets the first output power limit value to 0 W. That is, the first buck converter 130 outputs no power. With the engine rotation speed within this range, the second buck converter 140 also outputs no power as will be described later. With the engine rotation speed within this range, there is a possibility that the inter-terminal voltage of the capacitor 125 cannot be maintained in a range not lower than one half the inductive voltage of the AC generator 62. With the engine rotation speed within the range from 0 rpm to 650 rpm, the inter-terminal voltage of the capacitor 125 can be maintained at not lower than the output voltage of the first buck converter 130 by stopping the power output from the first buck converter 130 and the second buck converter 140, so that the AC generator 62 can be maintained in a power extractable state to thus prevent a power failure.

If the engine rotation speed falls within an engine rotation speed range of not lower than 650 rpm and lower than 1,000 rpm, the controller 86 sets the first output power limit value to 750 W. If the engine rotation speed falls within an engine rotation speed range of higher than 1,000 rpm, the controller 86 sets the first output power limit value to 1,200 W.

The controller 86 performs the output regulation control operation on the second buck converter 140 according to the engine rotation speed detected by the engine rotation speed sensor 59 and the actual output power of the first buck converter 130. Specifically, the controller 86 sets a second output limit value for the second buck converter 140 according to the engine rotation speed and the actual output power of the first buck converter 130, and regulates the output power of the second buck converter 140 at not higher than the second output limit value. The controller 86 may determine the actual output power of the first buck converter 130 based on the output signal of a current sensor 150 (see FIG. 11 , an example of the power sensor) that detects a current supplied from the first power line 81 to the first battery 91.

If the engine rotation speed falls within an engine rotation speed range of not lower than 0 rpm and lower than 650 rpm, the controller 86 sets the second output power limit value to 0 W. That is, the second buck converter 140 outputs no power. The reason for this is as described above.

If the engine rotation speed falls within an engine rotation speed range of not lower than 650 rpm and lower than 1,000 rpm, the controller 86 sets the second output power limit value to a value obtained by subtracting the actual output power of the first buck converter 130 from 750 W. Therefore, the total output power of the first buck converter 130 and the second buck converter 140 is 750 W. If the engine rotation speed falls within an engine rotation speed range of not lower than 1,000 rpm and lower than 1,500 rpm, the controller 86 sets the second output power limit value to a value obtained by subtracting the actual output power of the first buck converter 130 from 1,200 W. Therefore, the total output power of the first buck converter 130 and the second buck converter 140 is 1,200 W. If the engine rotation speed falls within an engine rotation speed range of not lower than 1,500 rpm and lower than 2,000 rpm, the controller 86 sets the second output power limit value to a value obtained by subtracting the actual output power of the first buck converter 130 from 2,300 W. Therefore, the total output power of the first buck converter 130 and the second buck converter 140 is 2,300 W. If the engine rotation speed falls within an engine rotation speed range of not lower than 2,000 rpm and lower than 3,000 rpm, the controller 86 sets the second output power limit value to a value obtained by subtracting the actual output power of the first buck converter 130 from 2,800 W. Therefore, the total output power of the first buck converter 130 and the second buck converter 140 is 2,800 W. If the engine rotation speed falls within an engine rotation speed range of not lower than 3,000 rpm and lower than 6,000 rpm, the controller 86 sets the second output power limit value to a value obtained by subtracting the actual output power of the first buck converter 130 from 4,200 W. Therefore, the total output power of the first buck converter 130 and the second buck converter 140 is 4,200 W. If the engine rotation speed falls within an engine rotation speed range of higher than 6,000 rpm, the controller 86 sets the second output power limit value to a value obtained by subtracting the actual output power of the first buck converter 130 from 4,700 W. Therefore, the total output power of the first buck converter 130 and the second buck converter 140 is 4,700 W.

Therefore, the total output powers of the first buck converter 130 and the second buck converter 140 are respectively equal or substantially equal to the output limit values shown in FIG. 10 , and conform to the characteristic line C3 shown in FIG. 5 . In FIG. 5 , the first output power limit values are shown by the stepwise characteristic line C1. The second output power limit values are each determined by subtracting the actual output power of the first buck converter 130 from the characteristic line C3. If the actual output powers of the first buck converter 130 are equal or substantially equal to the respective first output limit values, the second output power limit values conform to the stepwise characteristic line C2 shown in FIG. 5 . Of course, the first output limit values and the second output limit values are set as shown in FIG. 12 and as shown by the characteristic line C1 in FIG. 5 by way of example. If narrower engine rotation speed ranges are defined, for example, the first output limit values (i.e., the characteristic line C1) can conform more closely to the line L12 in the lower rotation speed range. Further, the total output power of the first buck converter 130 and the second buck converter 140 (i.e., the characteristic line C3) can conform more closely to the lines L28, L48 in the intermediate to higher rotation speed range.

In the present preferred embodiment, the total output power of the first buck converter 130 and the second buck converter 140 (see the characteristic line C3 in FIG. 5 ) thus substantially conforms to the line L12 in the lower rotation speed range from 0 rpm to 1,000 rpm, substantially conforms to the line L28 in the intermediate rotation speed range from 1,000 rpm to 2,000 rpm, and substantially conforms to the line L48 in the higher rotation speed range higher than 3,000 rpm. Therefore, the power can be extracted from the AC generator 62 at an efficiency comparable to that in the preferred embodiment shown in FIGS. 9 and 10 . In addition, the first battery 91 and the second battery 92 having different inter-terminal voltages can be charged with the power generated by the AC generator 62, making it possible to use a greater amount of power on the watercraft.

The rectifier regulator 70 is operative in the same manner as in the preferred embodiment shown in FIGS. 9 and 10 . Since the voltage to be outputted from the rectifier regulator 70 is not higher than 60 V, non-insulation type DC/DC converters which are smaller in size and lighter in weight can be used as the first buck converter 130 and the second buck converter 140.

As described above, the output powers of the first buck converter 130 and the second buck converter 140 are regulated so that the inter-terminal voltage of the capacitor 125 can be maintained in a range not lower than one half the inductive voltage of the AC generator 62. Specifically, if the engine rotation speed falls within the very low rotation speed range lower than 650 rpm, the first buck converter 130 and the second buck converter 140 outputs no power. Thus, the inter-terminal voltage of the capacitor 125 can be maintained at not lower than the output voltage of the first buck converter 130, so that the AC generator 62 can be maintained in the power extractable state to thus prevent the power failure.

In a preferred embodiment described above, the battery 90 is charged with the power generated by the AC generator 62, while the inductive voltage of the AC generator 62 is controlled so as to approach one half the inter-terminal voltage of the battery 90. Thus, the power generation efficiency of the AC generator 62 can be increased during the charging of the battery. This makes it possible to reduce the sizes and the number of the batteries 90 to be mounted on the watercraft 100. Therefore, more usable space may be provided in the watercraft 100. In addition, the watercraft 100 may have an improved movability such as the ability to accelerate and turn. Further, the watercraft 100 may have a reduced weight, such that the outboard motor 2 has an improved fuel efficiency. Furthermore, the power generation efficiency is improved to thus improve the fuel efficiency. Consequently, this reduces CO₂ emissions, thus making it possible to contribute to carbon neutrality and, thus, to achieve some of the SDGs.

While the preferred embodiments of the present invention have thus been described, the present invention may be embodied in some other ways. In a preferred embodiment described above, the second battery 92 is provided in addition to the first battery 91 on the hull 1 by way of example, but may be obviated if the electrical apparatuses 13 are not used on the watercraft. In a preferred embodiment described above, the outboard motors are used as the watercraft propulsion systems by way of example. The present invention is applicable to a watercraft propulsion system of other types using an engine as its drive source. Specifically, the present invention may be applied to an inboard motor, an inboard/outboard motor, a water jet propulsion system or the like. Further, the present invention may be applied to a power system to be used for a system other than the watercraft propulsion system, and including a generator driven by an engine and a battery to be charged by the generator.

While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims. 

What is claimed is:
 1. A watercraft propulsion system comprising: an engine; a propeller to be driven by the engine; a generator to be driven by the engine; a rectifier regulator connected to the generator; and a charging controller configured or programmed to control charging of a battery with power generated by the rectifier regulator such that an inductive voltage of the generator approaches one half an inter-terminal voltage of the battery.
 2. The watercraft propulsion system according to claim 1, wherein the battery includes a first battery having a first inter-terminal voltage, and a second battery having a second inter-terminal voltage that is higher than the first inter-terminal voltage; the watercraft propulsion system further comprises an engine rotation speed sensor to detect a rotation speed of the engine; and the charging controller includes a switch to connect the rectifier regulator to either one of the first battery and the second battery, and a controller configured or programmed to control the switch according to the engine rotation speed detected by the engine rotation speed sensor.
 3. The watercraft propulsion system according to claim 2, further comprising a first power line through which the switch is connected to the first battery, and a second power line through which the switch is connected to the second battery; wherein the charging controller further includes a boost converter connected between the first power line and the second power line and, when the switch connects the rectifier regulator to the first battery, the controller is configured or programmed to activate or deactivate the boost converter depending on a residual capacity of the first battery.
 4. The watercraft propulsion system according to claim 2, further comprising a first power line through which the switch is connected to the first battery, and a second power line through which the switch is connected to the second battery; wherein the charging controller further includes a buck converter connected between the first power line and the second power line and, when the switch connects the rectifier regulator to the second battery, the controller is configured or programmed to activate the buck converter.
 5. The watercraft propulsion system according to claim 1, further comprising an engine rotation speed sensor to detect a rotation speed of the engine; wherein the charging controller includes a capacitor connected between terminals of the rectifier regulator, a buck converter to reduce an inter-terminal voltage of the capacitor and output a voltage-reduced power to the battery, and a controller configured or programmed to regulate the output power of the buck converter according to the engine rotation speed detected by the engine rotation speed sensor.
 6. The watercraft propulsion system according to claim 1, wherein the battery includes a first battery having a first inter-terminal voltage, and a second battery having a second inter-terminal voltage that is higher than the first inter-terminal voltage; the watercraft propulsion system further comprises an engine rotation speed sensor to detect a rotation speed of the engine; and the charging controller includes a capacitor connected between terminals of the rectifier regulator, a first buck converter to reduce an inter-terminal voltage of the capacitor and output a voltage-reduced power to the first battery, a second buck converter to reduce the inter-terminal voltage of the capacitor and output a voltage-reduced power to the second battery, and a controller configured or programmed to regulate the output power of the first buck converter according to the engine rotation speed detected by the engine rotation speed sensor, and to regulate the output power of the second buck converter according to an actual output power of the first buck converter and the engine rotation speed detected by the engine rotation speed sensor.
 7. The watercraft propulsion system according to claim 1, wherein the water propulsion system includes an outboard motor.
 8. A watercraft comprising: a hull; a battery provided on the hull; and the watercraft propulsion system according to claim 1 provided on the hull.
 9. The watercraft according to claim 8, further comprising an electrical load provided on the hull and connected to the battery.
 10. A power system comprising: an engine; a generator to be driven by the engine; a rectifier regulator connected to the generator; a battery to be charged with power generated by the rectifier regulator; and a charging controller configured or programmed to control the charging of the battery with the power generated by the rectifier regulator such that an inductive voltage of the generator approaches one half an inter-terminal voltage of the battery.
 11. The power system according to claim 10, wherein the battery includes a first battery having a first inter-terminal voltage, and a second battery having a second inter-terminal voltage that is higher than the first inter-terminal voltage; the power system further comprises an engine rotation speed sensor to detect a rotation speed of the engine; and the charging controller includes a switch to connect the rectifier regulator to either one of the first battery and the second battery, and a controller configured or programmed to control the switch according to the engine rotation speed detected by the engine rotation speed sensor.
 12. The power system according to claim 11, further comprising a first power line through which the switch is connected to the first battery, and a second power line through which the switch is connected to the second battery; wherein the charging controller further includes a boost converter connected between the first power line and the second power line and, when the switch connects the rectifier regulator to the first battery, the controller is configured or programmed to activate or deactivate the boost converter depending on a residual capacity of the first battery.
 13. The power system according to claim 11, further comprising a first power line through which the switch is connected to the first battery, and a second power line through which the switch is connected to the second battery; wherein the charging controller further includes a buck converter connected between the first power line and the second power line and, when the switch connects the rectifier regulator to the second battery, the controller is configured or programmed to activate the buck converter.
 14. The power system according to claim 10, further comprising an engine rotation speed sensor to detect a rotation speed of the engine; wherein the charging controller includes a capacitor connected between terminals of the rectifier regulator, a buck converter to reduce an inter-terminal voltage of the capacitor and output a voltage-reduced power to the battery, and a controller configured or programmed to regulate the output power of the buck converter according to the engine rotation speed detected by the engine rotation speed sensor.
 15. The power system according to claim 10, wherein the battery includes a first battery having a first inter-terminal voltage, and a second battery having a second inter-terminal voltage that is higher than the first inter-terminal voltage; the power system further comprises an engine rotation speed sensor to detect a rotation speed of the engine; and the charging controller includes a capacitor connected between terminals of the rectifier regulator, a first buck converter to reduce an inter-terminal voltage of the capacitor and output a voltage-reduced power to the first battery, a second buck converter to reduce the inter-terminal voltage of the capacitor and output a voltage-reduced power to the second battery, and a controller configured or programmed to regulate the output power of the first buck converter according to the engine rotation speed detected by the engine rotation speed sensor, and to regulate the output power of the second buck converter according to an actual output power of the first buck converter and the engine rotation speed detected by the engine rotation speed sensor. 